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Westfälische Wilhelms-University Münster, Institute of Landscape Ecology, Robert-Koch-Str. ... pollinators of angiosperms (Corbet et al., 1991; Proctor et al., 1996). .... Peters, D. S., 1978, Archeriades gen. n., eine verhältnismäßig ursprüngliche ...
DIVERSITY, DISTRIBUTION PATTERNS AND ENDEMISM OF SOUTHERN AFRICAN BEES (HYMENOPTERA: APOIDEA) Michael Kuhlmann

Westfälische Wilhelms-University Münster, Institute of Landscape Ecology, Robert-Koch-Str. 26, D-48149 Münster, Germany, Email: [email protected]

Abstract:

An analysis of southern African bee diversity patterns based on 420 species reveals a bipolar pattern with highest species diversity located in the arid west of South Africa and the relatively moist east of the country. A detailed investigation of the distributions of 59 Colletes species shows a congruence of distribution areas of most species with seasonality of precipitation, a pattern that can be assumed for the majority of bee species. A total of 32 (sub)genera with about 256 species is strictly endemic to southern Africa with an exceptionally high number of endemic species (95%) strictly confined to the winter rainfall area.

Key words:

Southern Africa; bees; Apoidea; Colletes; biodiversity; biogeography; endemism

1.

INTRODUCTION

With an estimated 30,000 species worldwide, bees are the most important pollinators of angiosperms (Corbet et al., 1991; Proctor et al., 1996). Pollinators are essential for conservation of biodiversity in general and for food security because the majority of crop plants are pollinated by insects, especially by bees (API, 2003). Southern Africa and especially the Cape floristic region are renowned as a centre of phytodiversity of global importance but the bee fauna and pollinator-flower relationships are poorly investigated (Whitehead et al., 1987). Eardley (1989) found that at least 1600 species or one half of all bees described from subsaharan Africa occur in southern Africa, resulting in high species diversity similar to other known

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centres of bee diversity of the same size. However, detailed biogeographic information is largely lacking. In the present work a preliminary analysis of patterns of bee diversity, distribution and endemism in southern Africa is presented.

2.

MATERIALS AND METHODS

For a general analysis of diversity patterns in southern Africa, published and personal distribution records of 420 bee species of 50 genera were mapped on a 2° x 2° grid. For Colletes, the largest investigated genus, area maps were created for species with at least three records and species showing similar distributions are joined together in one map. The resulting patterns were compared with climatic factors (Schulze, 1997), phytogeography / -diversity, biomes and vegetation (Cowling et al., 1997).

3.

RESULTS AND DISCUSSION

3.1

Diversity patterns

On a global scale phytodiversity as well as bee diversity show an uneven distribution with plants best represented in moist tropical and subtropical regions (Barthlott et al., 1999). The centres of bee diversity are in xeric parts of the world with preference for mediterranean climates (Michener, 1979, 2000). The arid and semiarid west of South Africa is the only place on earth where a centre of bee diversity coincides with a phytodiversity hotspot (Capensis). This is interesting because many bee species are specialised (oligolectic) flower visitors suggesting that coevolutionary processes might be involved in speciation of both bees and flowers. In southern Africa the distribution of bee species diversity (Fig. 1) suggests a bipolar pattern with highest diversity located in the arid west of South Africa and the relatively moist east of the country. This pattern is influenced by the lack of investigations in the central and northern parts of South Africa as well as in large parts of Namibia, Zimbabwe and especially Botswana and Mozambique. Nevertheless, Eardley (1989) pointed out that the observed pattern very probably reflects the real situation.

Southern African Bees

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Figure 1. Number of bee species in southern Africa recorded on a 2°x 2° grid based on 420 species of 50 genera.

3.2

Distribution patterns

The species diversity pattern of the genus Colletes is largely identical to the one found for all investigated genera (Fig. 1). Thus, Colletes is used as a model to analyse distributions in more detail. For 59 of the 101 Colletes species known from southern Africa, a sufficient number of records were available to create distribution maps. The distribution of most species show in principle a congruence with seasonality of precipitation. The majority of Colletes (34 species, 58%) are limited to the winter rainfall area, some of them partly invading the southern Cape region with rain all year (Fig. 2). Four more widely distributed species of this group have their emphasis in the winter rainfall area or show disjunct distributions. Fourteen species (24%) are basically restricted to the early to mid summer rain area, partly invading adjacent areas and the southern Cape region with rain all year (Fig. 3). For the remaining 11 species a preference is not clearly recognisable. Six of them (10%) seem to have a preference for the late to very late summer rainfall area and the remaining five species (8%) are wide spread on the

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Figure 2. Distribution areas of 30 Colletes species that are strictly confined to the winter rainfall area and partly invade the southern Cape region with rain all year (climate data after Schulze, 1997).

subcontinent. Interestingly, the southern Cape region with rain all year does not have a specific fauna. No coincidence of bee distribution patterns is obvious for biome types, vegetation, phytogeographical regions or centres of phytodiversity. Patterns like the ones shown for Colletes can be assumed for most bee species in southern Africa.

3.3

Endemism

Of the 1600 bee species that occur in southern Africa about 85% are endemic (Eardley, 1989). Based on Michener (2000) an analysis of distribution patterns at generic level revealed that 32 (sub)genera with a total of 256 described species are strictly confined to this region. Especially the xeric winter rainfall area in western South Africa is a centre of endemism. About 95% of the bees that occur here are endemics (Eardley, 1989). Among them are some basal taxa of different families like the genera Scrapter

Southern African Bees

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Figure 3. Distribution areas of 14 Colletes species that are basically limited to the early to mid summer rain area and partly invade the southern Cape region with rain all year (climate data after Schulze, 1997).

(Colletidae) (Eardley, 1996), Fidelia and Fideliopsis (Engel, 2002), Afroheriades (Peters, 1978) and Aspidosmia (Peters, 1972) (Megachilidae) that are of special interest for the understanding of bee phylogeny and evolution. Intensive faunistic investigations in selected parts of this region reveal a high percentage of undescribed species even in recently revised genera that further emphasise its importance. The high degree of endemicity in the winter rainfall area is presumably linked to the fact that it is largely isolated by relatively moist regions to both the north and the east (Eardley, 1989). The moister eastern summer rainfall area of the subcontinent is not distinctly isolated from tropical Africa, thus, only about 75% of the bee species that occur here are endemic to southern Africa. Many bees of this region extend far north (e.g. East Africa) and often reach the southern extreme of their distribution in the Durban area (South Africa) (Eardley, 1989).

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Future Perspectives

The preliminary results presented here are only a first step towards a better understanding of diversity patterns, distribution and endemism of southern African bees. Currently the construction of the “Southern African Bee Data Base” (SouthABees) is under way to allow more comprehensive biogeographic study of distributions and to get further evidence for underlying factors and processes responsible for biogeographic patterns, speciation and endemicity.

REFERENCES API (African Pollinator Initiative), 2003, Plan of action of the African Pollinator Initiative, African Pollinator Initiative Sekretariat, Nairobi. Barthlott, W., Biedinger, N., Braun, G., Feig, F., Kier, G. and Mutke, J., 1999, Terminological and methodological aspects of the mapping and analysis of global biodiversity, Acta Bot. Fenn. 162:103-110. Corbet, S. A., Williams, I. H. and Osborne, J. L., 1991, Bees and the pollination of crops and wild flowers in the European Community, Bee World 72:47-59. Cowling, R. M., Richardson, D. M. and Pierce, S. M., 1997, Vegetation of southern Africa, Cambridge University Press, Cambridge. Eardley, C. D., 1989, Diversity and endemism of southern African bees, Bull. Pl. Prot. Res. Inst. 18:1-2. Eardley, C. D., 1996, The genus Scrapter Lepeletier & Serville (Hymenoptera: Colletidae), Afr. Ent. 4:37-92. Engel, M. S., 2002, Phylogeny of the bee tribe Fideliini (Hymenoptera: Megachilidae), with the description of a new genus from southern Africa, Afr. Ent. 10:305-313. Michener, C. D., 1979, Biogeography of the bees, Annls. Miss. Bot. Gard. 66:277-347. Michener, C. D., 2000, The bees of the world, Johns Hopkins University Press, Baltimore. Peters, D. S., 1972, Über die Stellung von Aspidosmia Brauns 1926 nebst allgemeinen Erörterungen der phylogenetischen Systematik der Megachilidae (Insecta, Hymenoptera, Apoidea), Apidologie 3: 167-186. Peters, D. S., 1978, Archeriades gen. n., eine verhältnismäßig ursprüngliche Gattung der Megachilidae (Hymenoptera: Apoidea), Ent. Germ. 4:337-343. Proctor, M., Yeo, P. and Lack, A., 1996, The natural history of pollination, Timber Press, Portland. Schulze, R. E., 1997, South African atlas of agrohydrology and –climatology, Water Research Commission, Pretoria. Whitehead, V. B., Giliomee, J. H. and Rebelo, A. G., 1987, Insect pollination in the Cape flora, S. Afr. Scient. Progr. Rep. 141:52-82.